Chain Saws in a Nature Preserve... What's going on??

by: Caroline Chan, Intern

Why are dozens of trees getting cut down in a nature preserve?  That’s a question you may find yourself asking the next time you hike the trails of the Los Trancos Open Space Preserve located along Page Mill Road above Palo Alto.  According to Mid-Peninsula Open Space District (MPOSD) Biologist Cindy Roesller, some trees are being cut down in an attempt to prevent the spread of a deadly plant disease known as Sudden Oak Death. 

Sudden Oak Death (SOD) is a disease that’s been sweeping through the forests of California since the mid 1990s and is now spreading to other states and countries as well. Phytophthora ramorum, the fungus-like pathogen (actually a water mold related to brown algae) that causes SOD, gets under the bark of trees such as tanoak, coast live oak, California black oak, Shreve’s oak, and canyon live oak and essentially girdles them by cutting off their nutrient and water supply.  Although the affected trees appear to die suddenly (some go from looking green and healthy to brown and dead or dying in a matter of weeks), it may take up to 2 years for a tree to succumb to the disease after being initially infected. 

The disease also affects the leaves and twigs of numerous other plants such as madrone, huckleberry and bay trees.  Although these “host” plants usually don’t die from the disease, they provide a place for the pathogen to “hang out” and spread via wind or water.  Studies suggest that if bay tree leaves are located within 15 feet of the trunk of an oak tree that the oak tree is much more likely to become infected with SOD.  That is why the MPOSD has decided to clear away some of the bay trees that are in close proximity to several of the ancient oaks at Los Trancos.  Select oak trees are also being sprayed with Agri-Fos, a phosphonate compound that is applied annually to the trunks of healthy trees and is believed to help boost a trees ability to ward off disease.  Studies are also underway to find and propagate oak trees that are resistant to the disease with the intent to eventually plant them in areas that are heavily affected by SOD. 

So what can you do to help stop the spread of this deadly disease?  Clean the big clods of mud from your shoes (there’s a boot brush at Los Trancos for this), mountain bike & vehicle tires, horse hooves and animal paws before leaving an area where SOD is present.  Familiarize yourself with the symptoms and plants that are affected (look for thick dark red tree sap oozing from the bark and staining the trunk of the tree, trees with brown leaves hanging on them and/or the presence of a fungus called Hypoxylon that often invades trees that are weakened by SOD).  Inspect any nursery plants you buy for signs of disease (SOD is thought to be an exotic disease which initially escaped from nursery plants imported from Asia).  Finally, follow the regulations that are listed for dealing with plants infected with SOD on the California Oak Mortality Task Force website:


Sudden Oak Death Informational Talk given to the Environmental Volunteers by Mid-Peninsula Open Space District Biologist Cindy Roesller on 2/17/10 at the MPOSD Field Office. 

California Oak Mortality Task Force website:

Photo Credit: Brittany Sabol